1. Field of the Invention
The present invention relates to a planar heater, more particularly to a planar heater in which a carbon wire heat generator is sealed in a silica glass plate-like member, and to a planar heater preferably used in a heat treatment for a wafer in a semiconductor manufacturing process.
2. Description of the Related Art
In semiconductor manufacturing processes, various heat treatments are performed to a silica wafer and the like in the steps. These heat treatments require severe temperature management, and a heat treatment atmosphere is required to maintain clean atmosphere in which particles such as dust are not present.
For this reason, a heater used in a heat treatment requires good temperature uniformity and good temperature rising/dropping controllability, and needs to satisfy various conditions such as a condition that a contamination material such as particles are not emitted. As one of these semiconductor manufacturing heaters, a heater having a structure in which a heat generator and a non-oxide atmospheric gas are sealed in a supporting member such as a silica glass member is known.
The present inventors developed a semiconductor heat treatment apparatus heater as a very preferable semiconductor manufacturing heater in which a carbon wire heat generator fabricated by weaving a plurality of carbon fiber bundles each obtained by bundling extra fine carbon fibers is sealed in a supporting member such as a silica glass member together with a non-oxidizing atmospheric gas and have filed the heater as Japanese Patent Application Laid-Open No. 2007-220595.
The heater described in Patent Document 1 will be described below with reference to FIGS. 9 to 11. FIG. 9 is a plan view showing a planar heater, FIG. 10 is a side view of a planar heater shown in FIG. 9, and FIG. 11 is a sectional view along an I-I line in FIG. 10.
As shown in FIGS. 9 and 10, in a planar heater 100, a heating surface 101 is circular planarly formed, and a carbon wire heat generator CW is sealed in a silica glass plate-like member 102. The silica glass plate-like member 102 includes a first silica glass member 102a, a second silica glass member 102b, and a third silica glass member 102c. 
The upper and lower surfaces of the first silica glass member 102a and the third silica glass member 102c are planarly formed. On the other hand, in the upper surface of the second silica glass member 102b, a trench 102d having the same shape as that of an arrangement pattern shown in FIG. 9 is formed. In the lower surface of the second silica glass member 102b, trenches 102e1 and 102e2 radially extending from the center are provided.
On the planar heater 100, as shown in FIG. 9, the heating surface 101 is divided into four regions A, B, C, and D. More specifically, a carbon wire heat generator CW is arranged in each of the regions A and B which are regions obtained by dividing an inside region of the heating surface 101 by two and furthermore, the regions C and D which are regions obtained by dividing an outside region positioned on the circumference of the inside region of the heating surface 101.
The trench 102d in the inside regions (region A and region B) of the heating surface 101 communicates with a through hole formed in positions a and b of the central portion on the heating surface 101. On the other hand, the trench 102d in the outside regions (region C and region D) of the heating surface 101 communicate with a through hole formed in outer circumferential positions e and f of a heating surface 101a. 
One end of the trench 102e1 communicates with a through hole formed in a position c of the central portion on the heating surface 101, and the other end communicates with the through hole formed in the position e of the outer circumferential portion of the heating surface 101. Similarly, one end of the trench 102e2 communicates with a through hole formed in a position d of the central portion on the heating surface 101, and the other end communicates with the through hole formed in the position f of the outer circumferential portion of the heating surface 101.
The carbon wire heat generator CW is contained in the internal portion of the trench 102d in the inside regions (region A and region B) and the outside regions (region C and region D), a connection line 103b is contained in the trench 102e1, and a connection line 103a is contained in the trench 102e2.
Furthermore, at the lower central portion of a first silica glass member 2a, as shown in FIGS. 10 and 11, an electric power supply terminal unit 108 having connection lines 103a, 103b, 104a, and 104b energized to the carbon wire heat generator CW is arranged. The connection lines 103a and 103b are connection lines to energize the regions C and D of the outside regions, and the connection lines 104a and 104b are connection lines to energize the center portion side regions A and B.
As shown in FIGS. 10 and 11, the connection line 103a is contained in a silica glass tube 105a, and the connection line 103b is contained in a silica glass tube 105b. The silica glass tubes 105a and 105b which contain the connection lines 103a and 103b pass through the first silica glass member 102a to be brought into contact with the lower surface of the second silica glass member 102b. 
Therefore, the connection line 103a enters the trench 102e2 from the silica glass tube 105a at the position d, and is connected to carbon wire heat generators CWC and CWD in the regions C and D of the outside regions through a through hole at the position f. Similarly, the connection line 103b enters the trench 102e1 from the silica glass tube 105b at the position c, and is connected to the carbon wire heat generator CW in the regions C and D of the outside regions through a through hole at the position e.
The connection line 104a is contained in silica glass tube 106a, and the connection line 104b is contained in a silica glass tube 106b. The silica glass tubes 106a and 106b pass through the first silica glass member 102a to be brought into contact with an internal portion bottom surface in which a through hole formed in the second silica glass member 102b opens. Therefore, the connection line 104a passes from the silica glass tube 106a through a through hole at the position a, and is connected to the carbon wire heat generator CW in the center portion side regions A and B. The connection line 104b passes from the silica glass tube 106b through a through hole at the position b, and is connected to the carbon wire heat generator CW in the center portion side regions A and B.
End portions of all the silica glass tubes 105a, 105b, 106a, and 106b which contain the connection lines 103a, 103b, 104a, and 104b are sealed and contained in the internal portion of a large-diameter silica glass tube 107.
In this manner, since the connection lines 103a, 103b, 104a, and 104b are concentrated on a central portion on a rear surface of the heating surface 101 and configured as the power supply terminal unit 108, a compact heat generator can be achieved. A heater obtained by sealing the heat generator in a clean heat-resistant support member such as a high-purity silica glass member together with a non-oxidizing gas does not generate particles or the like, and are very preferably used as a semiconductor manufacturing heater as described above.
In the meanwhile, Radiant heat from the carbon wire heat generator CW is propagated to not only the heating surface 101 of the planar heater but also to the lower side of the planar heater 100. In particular, a lower end portion of the large-diameter silica glass tube 107 is attached to a flange or the like of a casing through an O ring. For this reason, radiant heat from the carbon wire heat generator CW passes through the internal portion of the large-diameter silica glass tube 107, is propagated to the O ring, and deteriorates the O ring to pose a technical problem.